Systems providing power inductively to moving vehicles along roadways have been discussed and developed for many years. Solutions such as that disclosed in patent publication PCT/NZ 2010/000159 propose a roadway including a plurality of embedded inductive loops; these loops may be energised when a vehicle requiring charge is determined to be in the proximity. One of the challenges in such a system is determining when a vehicle is in proximity with the embedded inductive loops with sufficient accuracy, sensitivity and robustness. Such a detection system must also be able to tolerate the typical misalignments expected in an inductive system involving electric vehicles. Vehicle sensing devices have been developed for other uses involving roadways and systems have been proposed for electric vehicle charging systems. However previously demonstrated systems lack the required accuracy and efficiency for an effective roadway powered electric vehicle system.
A proposed vehicle detection involving a magnetic field created by the road and using the metal bulk of the car as a means for detection, as described in EP01993298 A2, allows for rough detection of moving vehicles. These systems require magnetic fields to be present over the road at all times and are not sensitive to the type of vehicle or inductive charging pads on that vehicle. The system is also open to outside interference and does not generate an accurate position of where the car is. This is particularly problematic with respect to electric vehicles because it is desirable to have the charging pads switched on only when the electric vehicles pads are directly above the charging pads for improved efficiency and safety. An alternative embodiment, as described in US20110198176 uses the induction of voltages in a track, from stray magnetic fields in a train, to detect the train. This system does not provide the indication of a suitable vehicle nor the required precision for most electric vehicle roadway charging systems.
More complex systems for vehicle detection have also have been considered, including systems involving RFID, GPS or infrared detection for example PCT/NZ/2010/000159 proposes using an RFID tag in the electric vehicle as a way to detect the presence of the electric vehicle and control the system. Such systems are complex, they require more control and sensing devices must be positioned in or near the roadway. Furthermore, such systems are typically too slow for moving traffic and do not provide the required detection accuracy. These systems also require the car to tell the road when it is present and to control the switching of the pads. This adds further time and complication to the system and reduces the ability of the road controller to operate an efficient system. Further issues arise in such vehicle detection applications due to the large inductive power transfer signals that are occurring at the same or similar time.